Method of connecting optical waveguide and optical fiber

ABSTRACT

A method of connecting waveguides and optical fibers includes the steps of forming the waveguides and a marker at the same time on a waveguide substrate when patterning the waveguides by a photolithography method, forming a clad layer on a region other than another region when the marker is formed so as to embed the waveguides, and forming a fitting pin groove at a position corresponding to a position of the marker. By using this fitting pin groove, a waveguide module and an optical fiber connector are connected so as to connect each of the waveguides and each of the optical fibers with each other. With this method, waveguides and optical fibers can be aligned and connected with each other easily and in a short period of time without employing an expensive aligning device.

TECHNICAL FIELD

The present invention relates to a method of connecting opticalwaveguides and optical fibers used in an optical communication system.

PRIOR ART

In general, waveguide elements are used as optical members to constitutean optical communication system. The waveguide elements are categorizedmainly into two types, i.e., one type in which a waveguide is formed bystacking silica glass layers each having different refractive index oneon another on an Si substrate, for example, and the other in which awaveguide is formed by stacking semiconductor thin films each having adifferent composition on a special semiconductor substrate made of GaAs,LiN, or the like.

In order to use these silica type waveguides and semiconductor typewaveguides as optical members in an optical communication system, thewaveguides must be connected to optical fibers so as to input/outputlight. More specifically, a waveguide and an optical fiber must beconnected such that the pattern of a cross section of the waveguide andan arrangement of the optical fibers are aligned with each other.

One of the examples of such a connecting method will now be described inconnection with a case where a 1×8 splitter chip of a silica typewaveguide and an optical fiber are connected with each other.

A 1×8 splitter chip 12 such as shown in FIG. 1 (A) in which input/outputwaveguides 11 are formed on a silicon substrate 10 is fixed in atub-like metal casing 13 by adhesive as shown in FIG. 1 (B), and thecasing is annealed to make a waveguide part. Then, an input-side opticalfiber connector 15, in which an optical fiber 14 is put through andwhich can be moved at a degree of freedom of 6, is arranged to face anend face of the casing 13, as can be shown in FIG. 1 (C). Thereafter, asshown in FIG. 1 (D), the position of the input-side optical fiberconnector 15 is adjusted such that the optical output from each of theoutput waveguides 11 of the chip 12, as the result of light madeincident from the optical fiber 14, has the maximum value. At the mostappropriate position, the input waveguide 11 and the core of the opticalfiber 14 are aligned with each other along the optical axis, and fixedlyconnected with each other by use of YAG laser, adhesive, or the like.

Next, as shown in FIG. 1 (E), an output-side optical fiber connector 16in which eight optical fibers 14 are fixedly arranged in parallel at thesame pitch as that of the output waveguides 11 of the chip 12, is madeto face the other end face 13b of the casing 13. Following this, asshown in FIG. 1 (F), the output-side optical fiber connector 16 is movedat a degree of freedom of 6 such that the optical output from each ofthe eight optical fibers has the maximum intensity of output. At themost appropriate position, the output waveguides 11 and the core of theoptical fiber 14 are aligned with each other along the optical axis, andfixedly connected with each other by use of YAG laser, adhesive, or thelike. In general, connection of a waveguide and an optical fiber iscarried out in the above-described manner.

However, in the case of the above-described case, there is noestablished standard of alignment between a waveguide formed in awaveguide element and an optical fiber running through an optical fiberconnector, and a judgment as to whether there is an error in axisalignment is simply based on the level of the intensity of the outputlight resulted by incidence of light into the optical fiber. Thus, thereliability of the connection is low.

Further, according to the above-described method, it takes at least onehour to connect a casing end face and an optical fiber connector alignedwith each other for one connection, and therefore this method is notsuitable for mass production. Also, an extremely expensive alignmentfixing device is required.

DISCLOSURE OF THE INVENTION

The purpose of the invention is to provide a method of connecting awaveguide and an optical fiber, in which the waveguide and the opticalfiber are aligned with each other easily in a short period of timewithout using an expensive alignment fixing device.

The purpose can be achieved by a method of connecting a waveguide and anoptical fiber, characterized by comprising the steps of forming awaveguide and a marker simultaneously on a waveguide substrate whenpatterning the waveguide by the lithography method; forming a clad layeron the region other than that of the marker so as to cover thewaveguide; forming a groove for a fitting pin at a position with respectto the marker, and connecting a waveguide module and an optical fiberconnector by use the groove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 (A), 1 (B), 1 (C), 1 (D), 1 (E) and 1 (F) are explanatorydiagrams each showing a step in a conventional method of connecting awaveguide and an optical fiber;

FIGS. 2 (A), 2 (B), 2 (C), 2 (D), and 2 (E) are explanatory diagram eachshowing a step of manufacture of a waveguide chip used in the methodaccording to the present invention;

FIG. 3 (A) is a plan view of an optical fiber core block used in themethod according to the invention, FIG. 3 (B) is a front view of thecore block shown in FIG. 3 (A), and FIG. 3 (C) is a side view of thecore block shown in FIG. 3 (A);

FIGS. 4 (A), 4 (C), and 4 (E) are diagrams each showing a plan view of aconnecting portion, and designed to illustrate the connecting methodaccording to the invention, and FIGS. 4 (B), 4 (D), and 4 (F) arediagrams showing side views of the connecting portions shown in FIGS. 4(A), 4 (C), and 4 (E), respectively;

FIG. 5 is a plan view of a 1×8 tree splitter waveguide chip according tothe invention;

FIG. 6 is a cross section of the waveguide chip shown in FIG. 5, takenalong the line A--A;

FIG. 7 is a plan view of a 1×8 tree splitter waveguide chip processed tohave v-shape grooves according to the invention;

FIG. 8 is a side view of the waveguide chip shown in FIG. 7, taken fromthe light outputting face side;

FIG. 9 is a schematic view of a substrate of a waveguide moduleaccording to the invention;

FIG. 10 is a side view of the waveguide module according to theinvention, taken from the light outputting face side;

FIG. 11 is a schematic view of an optical fiber connector according tothe invention;

FIGS. 12 (A) and 12 (B) are respectively a plan view and side view of awaveguide module connecting fiber and waveguide to each other accordingto the method of the invention;

FIGS. 13 (A) and 13 (B) are top front views of a waveguide substrate onwhich a waveguide core and marker are formed, in a step of themanufacturing process of a waveguide module according to the firstembodiment of the invention;

FIG. 14 is a cross section of the waveguide substrate shown in FIG. 13.

FIG. 15 (A) and 15 (B) are top front views of the waveguide substrate,designed to illustrate the embeded region of the waveguide substrate;

FIG. 16 is a cross section of the waveguide substrate on which a v-shapegroove is formed;

FIG. 17 is a cross section of the waveguide module assembled;

FIGS. 18 (A), 18 (B) and 18 (C) are diagrams illustrating how thewaveguide module and the optical fibers are connected; and

FIG. 19 is a schematic view showing an optical fiber connectormanufactured by the plastic molding method according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples of the invention will now be described in detail with referenceto accompanying drawings.

EXAMPLE 1

A waveguide chip was manufactured in the following manner.

As can be seen in FIG. 2 (A), an SiO₂ layer 21 serving as an lower cladlayer was formed on a silicon substrate 20 by the flame hydrolysisdeposition method. Then, as shown in FIG. 2 (B), the SiO₂ layer 21 wascoated with SiO₂ +TiO₂, waveguide materials, by the flame hydrolysisdeposition method, to form a waveguide layer 22. A material other thansilicon such as ceramic, semiconductor material, glass, or the like, canbe used as a material of the substrate.

The waveguide layer 22 was subjected to patterning by the generalphotolithography method so as to form a waveguide circuit (planerwaveguide circuit) 23 and marker 24 as shown in FIG. 2 (C). Morespecifically, a resist layer (not shown) was formed on the waveguidelayer 22, and the layer was etched by use of a mask having a pattern forthe waveguide circuit 23 and the marker 24, followed by removal of theresist layer.

Next, as shown in FIG. 2 (D), SiO₂ was deposited by the flame hydrolysisdeposition method using a mask 25 arranged above a region covering themarker 24 on the SiO₂ layer 21 in which the waveguide circuit 23 and themarker 24 were formed, so as to form a upper clad layer. Thus, awaveguide chip 1 as shown in FIG. 2 (E) was manufactured.

Manufacture of an optical fiber core block, i.e. optical fiber block,will now be described.

A plate made of single-crystal silicon was processed at a high accuracysuch that the top surface and the bottom surface are exactly in parallelwith each other, thereby obtaining a substrate. Then, as shown in FIGS.3 (A), 3 (B) and 3 (C), eight optical fiber V-shaped grooves 31 and amarker V-shaped groove 32 were formed in the substrate 30. The V-shapedgrooves 31 were formed such that a distance Y₁ between the core portions34 of optical fibers located in grooves adjacent to each other is thesame as the distance between the centers of waveguide circuits 23adjacent to each other, so as to align a core portion 34 and acorresponding waveguide circuit 23 of a chip with each other. The markerV-shaped groove 32 was located at such a position that a distance Y₂between the core portion 34 of the extremely right optical fiber and thecenter portions of the marker V-shaped groove 32 was the same as thedistance between the center of the extremely right waveguide circuit 23and the center of the marker 24, so as to align the marker 24 and theV-shaped groove 32 with each other.

An optical fiber 33 was provided in each of the optical fiber V-shapedgrooves 31 formed on the substrate 30, and an optical fiber press plate35 was provided on the region covering the optical fiber V-shapedgrooves 31, thereby manufacturing an optical fiber core block 2.

An example of connection between the waveguide chip 1 and the opticalfiber core block 2 will be described.

As shown in FIGS. 4 (A) and 4 (B), a waveguide chip 1 and an opticalfiber core block 2 were formed on a support plate 40 the surface ofwhich was processed to be flat. The waveguide chip 1 and/or the opticalfiber core block 2 may be fixed onto the support plate 40 by means ofadhesive or the like.

Next, as shown in FIGS. 4 (C) and 4 (D), the connecting face of thewaveguide chip 1 and that of the optical fiber core block 2 were broughtto face with each other. Then, a pressure was applied to the directionindicated by the arrow shown in FIG. 4 (D), and while pressing thewaveguide chip 1 and the core block 2 against the supporting plate 40,the core block 2 was moved in the directions indicated by the arrowsshown in FIG. 4 (C). This operation was repeated until the center of themarker 24 of the waveguide chip 1 and the center of the marker V-shapedgroove 32 of the optical fiber core block 2 were aligned with eachother. Thus, alignment of the waveguide circuits 23 of the waveguidechip 1 with the core portions 34 of the optical fibers 33 was carriedout, and then the waveguide chip 1 and the core block 2 were fixed ontothe supporting plate 40 by means of adhesive or the like, as shown inFIGS. 4 (E) and (F). It should be noted that after the waveguide chip 1and the optical fiber core block 2 are fixedly connected with eachother, the supporting plate 40 may be removed.

In this embodiment, SiO₂ +TiO₂ were used as the material of thewaveguide, and the waveguide layer was formed by the flame hydrolysisdeposition method, but some other waveguide material or other formingmethod may be used to achieve the same advantage of the invention.

EXAMPLE 2

As shown in FIG. 6, a silica glass underlaying clad layer 51 was formedon a 1-mm-thick 3-inch silicon substrate 50 by the flame hydrolysisdeposition method. The assembly was processed into a 3-dimensionalwaveguide structure as shown in FIG. 5, by semiconductor fine processingtechniques such as photolithography and dry etching. Thus, eightwaveguide circuits 52 and two pairs of V-shaped groove marker 53 wereformed simultaneously on the silicon substrate 50. The V-shaped groovemarker 53 sets the standards of position and height for a V-shapedgroove, which will be described later.

Next, an upper clad layer 55 was formed by the flame hydrolysisdeposition method such that only the waveguide circuit 52 was embedded.Since the V-shaped marker 53 serves as a standard for processing aV-shaped groove, it was not embedded. There are methods as that in whicha particular section is not embedded, for example, the method whereinflame hydrolysis deposition is carried out with a mask such as a siliconplate covering the section. In FIG. 5, reference numeral 54 denotes thebottom of the V-shaped groove formed later by a cutting process.

As shown in FIG. 7, a waveguide circuit 52 includes combinations of Ybranches, and has a 1×8 tree splitter structure in which one inputwaveguide 56 is branched out into eight output waveguides 57. Eight ofsuch a structure are continuously formed on the silicon substrate 50.The eight output waveguides 57 in the output section are arranged inparallel with each other with an interval of 250 μm between an adjacentpair. The waveguide circuit has a structure such as shown in FIG. 6.More specifically, the core 58 of the waveguide circuit has a 8 μmsquare, and the circuit has a difference in specific index of refractionof 0.3%, and are compatible with a single mode fiber.

The V-shaped groove marker 53 has a structure such as shown in FIG. 6.More specifically, two lines 53a and 53b each having a width of 10 μmand a length of 30 mm, and a line 53c having a width of 3 mm, and alength of 20 mm are arranged in parallel with each other with aninterval of 10 μm. Further, as shown in FIG. 5, a set of this structureis provided on both sides of the eight waveguide circuits 52.

Thereafter, a silicon substrate 50 supported by a vacuum chuck issubjected to cutting process by use of a slicer or the like, to make agroove having substantially a V-shape (to be called a V groovehereinafter). Alignment of a V groove 59 with waveguides 56 and 57 isbased on the position of the V-shaped groove marker 53 provided on thesilicon substrate 50. The alignment is carried out by specifying theposition on the top surface of the substrate by image processing using aCCD camera, and the level of the upper surface of the core 58 by use ofa capacitance type displacement gauge. A V groove 59 formed by thecutting process has a angle of the v section (the bottom portion) ofabout 60°, and a depth of about 700 μm. The groove 59 was formed suchthat the center of the core 58 is at the same level as the center of thefitting pin 61 having a diameter of 0.7 mm when placed in the groove, asshown in FIG. 8. Further, there were two of V grooves 59 arranged 4.6 mmaway from each other, with the waveguides 56 and 57 interposedtherebetween.

The silicon substrate 50 thus obtained was sliced into eight chips byuse of a dicing saw, thereby obtaining lower substrates 60 on each ofwhich a V groove 59, waveguides 56 and 57 were formed. Each chip had awidth of 6.4 mm, and a length of 50 mm.

A ceramic substrate was subjected to cutting process by use of a slicerto form two grooves 63 each having substantially a trapezoid shape suchas to press the upper surface of a fitting pin 61. Then, the substratewas divided by a dicing saw into a predetermined number of chips, eachof which serves as a press cover 62. Each chip had a width of 6.4 mm,and a length of 50 mm.

Next, as shown in FIG. 9, a lower substrate 60 was fixed to a fixationbase 66 by adhesive, and four substrate fixation pins 64 each having adiameter of 0.7 mm and a length of 8 mm were placed on V-grooves 59 ofthe lower substrate 60. Each of the substrate fixation pins 64 wasarranged such that the middle portion thereof was located at a position12 mm away from an end 60a or 60b of the surface of the siliconsubstrate. Following this, as shown in FIG. 10, a press cover 62 wasplaced on the lower substrate 60, and they are fixed together withadhesive or clamped together by a clamp spring 65, thereby manufacturinga waveguide module 4.

Manufacture of an optical fiber connector will now be described.

As shown in FIG. 11, a lower substrate 70 made of ceramic was subjectedto cutting process by use of a slicer, so as to form an optical fiber Vgroove 71 for supporting an optical fiber, and fitting pin V grooves 72on both sides of the V groove 71. The grooves 71 and 72 were formed suchthat the position of each of the optical fiber V groove 71 and thefitting pin V groove 72 corresponds to that of each of the core 58 andthe V groove 59 in the end face 60b of the lower substrate 60. Theoptical fiber V groove 71 thus formed had an angle of the V portion of60° and a width of 210 μm. The pitch between adjacent optical fiber Vgrooves 71 was set at 250 μm. The fitting pin V groove 72 had an angleof the V portion of 60° and a width of about 700 μm. The V groove 72 waslocated such that the core center of each of optical fibers 73, whichwill be described later, and the center of each of the fitting pins 61were leveled with each other. There were two fitting pin V grooves 72arranged 4.6 mm away from each other, interposing the optical fiber Vgrooves 71 therebetween.

In a similar manner as that of the press cover 62, a connector presscover 74 was manufactured by also forming two grooves each havingsubstantially a trapezoid shape such as to cover the top surface of afitting pin 61, on a ceramic substrate by cutting process.

A ribbon-like 8-core single mode fiber 73 having an outer diameter ofeach fiber of 125 μm and an interval pitch of adjacent fibers of 250 μmwas placed on the optical fiber V grooves 71 of the lower substrate 70,and the press cover 74 was fixedly mounted on the lower substrate 70 byepoxy adhesive. Then, the end face 70a was polished by mirror-likefinishing, thereby completing an optical fiber connector 5. In thisexample, a single-core optical fiber connector to be connected to theoutput end 60b of the waveguide module 4 was manufactured in a mannersimilar to the above-mentioned.

After that, as shown in FIGS. 12 (A) and 12 (B), four fitting pins 61were inserted into two V grooves 59 of the waveguide module 4, and thefitting pins 61 were fit into the fitting pin V grooves of a multi-coreor single-core optical fiber connector 5 for alignment. Thus, theoptical fiber connector 5 was arranged such that both ends of thewaveguide module 5 were brought into contact with the optical fiberconnectors 5. The interface was coated in advance with matching oil ormatching grease so as to prevent loss due to Fresnel reflection. Then, apress spring 76 is inserted into a fixation base 66 to apply some weighton the interface.

As described, in this example, the waveguide module and the opticalfiber connector are connected with each other by means of fitting pins,and therefore alignment between a waveguide and a guide groove formed ona lower substrate, and an optical fiber and a guide groove or guide holein the optical fiber connector can be accurately performed. Thus, thewaveguide module and the optical fiber connector can be connected witheach other easily in a short period of time. In this example, thewaveguide element and the optical fiber connector are detachablyconnected. Consequently, waveguide modules each having a differentpattern can be connected to an optical fiber connector withoutperforming alignment along with an optical axis.

A waveguide element and an optical fiber connector manufactured in thisexample were connected with each other so as to examine its connectionin terms of connection loss. The connection loss was an average of 0.5dB, with a maximum of 1 dB, and thus it was confirmed that alignmentdeviations between waveguides and optical fibers can be suppressed, andconnection of them can be carried out at a small loss, according to thepresent invention.

EXAMPLE 3

A lower clad layer 81 and a core layer were formed on a siliconsubstrate 80 by the flame hydrolysis deposition method so as tomanufacture a slab waveguide. Then, as shown in FIG. 13 (A) and FIG. 14,a core layer was patterned by photolithography and dry etching so as toform four waveguide cores 82 and eight markers 83, one marker 83 beingformed on either side of each waveguide core 82. Further, as shown inFIG. 13 (B), ribbon-like markers each having a width of 2.5 mm and alength of 50 mm were formed such as to run across the markers. Thephotomask used by the photolithography had both waveguide core patternand marker pattern.

Next, an upper clad layer 84 was formed on a embeded including waveguidecores 82, as shown in FIGS. 15 (A) and 15 (B), to embed the waveguidecores 82. Since the markers 83 were to be used for alignment of aV-shaped groove to be formed later, particular portions of the markerswere left uncovered by the upper clad layer 84. This can be achieved,for example, by depositing an upper clad layer by flame hydrolysisdeposition method with a portion of each of the marker 93 being coveredby a silicon plate or the like.

Then, the silicon substrate 80 is subjected to cutting process by use ofa slicer, so as to form V grooves 85 thereon. As shown in FIG. 16, one Vgroove 85 was formed such that the center of the groove 85 was alignedwith the center of each of the markers, and the depth of the V groove 85was adjusted such that the center of each marker 83 was aligned with thecenter of the cross section of a fitting pin 86 when placed on the Vgroove 85. Lastly, the substrate 80 was sliced into chips, therebyobtaining a plurality of waveguide elements 6.

Thereafter, the silicon substrate 80 was subjected to cut process usinga slicer to form a V-shaped groove 85. More specifically, the cuttingprocess was performed such that the center position of the V-shaped ofthe groove 85 was aligned with the center of each marker 83, and thedepth of the V-shaped groove 85 was adjusted such as to match the centerof each marker 83 with the center of fitting pin 86 to be inserted intothe V-shaped groove 85. FIG. 16 is a diagram showing a cross section ofa wafer sample after formation of the V-shaped groove. In order toillustrate a cross section of the structure of the buried and non-buriedregions, the portion of the sample where buried and non-buried regionsappear on both sides of the V-shaped groove, was selected. The structurecan be observed when the wafer as shown in FIG. 15 (A) and 15 (B) isdiagonally cut. It should be noted that when the wafer is cut verticallywith respect to the V-shaped groove, a structure in which both sides ofthe V-shaped groove are buried can be observed.

Then, the obtained waveguides were diced by a dicing saw, and thus, anumber of waveguides elements 8 were obtained.

A waveguide element 6 thus obtained and a silicon substrate 87 on whichgrooves were formed by the cutting process mentioned before, wereassembled together while fitting a fitting pin in each of the grooves,and fixed with each other by means of a spring 88 as shown in FIG. 17,or adhered with each other by adhesive, thereby completing a fittingwaveguide module 7. A fitting waveguide module 7 as shown in FIG. 18 (A)and an optical fiber connector 8 shown in FIG. 18 (B) were connectedwith each other as shown in FIG. 18 (C), and the connection was examinedin terms of connection loss. The result indicated that they wereconnected at a connection loss of as low as 0.3 dB-1.0 dB.

EXAMPLE 4

A low substrate 60 was manufactured by a method similar to that ofExample 2, and both end faces 60a and 60b thereof were polished. Thesubstrate 60 was fixed onto a fixation base 66 by adhesive. Then, fourfitting pins 61 were placed on V grooves 59 such that the center of eachfitting pin 61 was leveled with the center of waveguide 56 or 57 in eachend face. While pressing each fitting pin 61 against each V groove 59such that the pin is brought into tight contact with the two sides ofthe V groove, and each fitting pin 61 was fixed to the lower substrate60 by adhesive, thereby manufacturing an optical waveguide module 4.

An optical fiber connector 5 was brought to face to each of the endfaces of a waveguide module 4 while aligning them with each other bymeans of an fitting pin 61. Further, adhesive was applied onto each endface, and the waveguide module 4 and the optical fiber connectors wereconnected with each other by hardening the adhesive by heat as beingpressed with each other.

Waveguide module and optical fiber connectors manufactured according tothis example were subjected to a connection test so as to examine theconnection of each sample in terms of connection loss. The connectionloss was an average of 0.5 dB, with a maximum of 1 dB.

Next, an optical fiber connector and a waveguide-use press cover weremanufactured from glass ceramic which transmits the light in a range of350 nm-450 nm at a transmissibility of 20% or higher. Adhesive used foreach interface here was of a Uv setting type having an index ofreflection of 1.456, which is close to that of silica glass, by whichthe Fresnel reflection at the interface can be small as small aspossible. Thus, a UV light was irradiated on the interface from above.

With this method, similar results to those of the above connection testwere obtained. Further, the manufacturing time was significantlyshortened as compared to that case where the thermosetting type adhesivewas used.

EXAMPLE 5

In place of ceramic, silicon was used as a material for an optical fiberconnector, and subjected to cutting process by use of a slicer so as toform V grooves 71 and 72. Optical fibers thus formed were assembled asin Example 2, and subjected to a test so as to examine its connection interms of connection loss. The initial values thereof were similar tothose of Example 2, and thus it was confirmed that the optical fibersmanufactured as above can be connected with each other at a connectionloss of an average of 0.5 dB, with a maximum of 1 dB.

The connected optical fiber connectors were subjected to a heat cycletest, and the loss variation obtained in the test carried out at atemperature of from -10° C. to -60° C., was within a range of ±0.2 dB.As compared to the result obtained with the ceramic-made optical fiberconnector, i.e., a loss variation of 0.5 dB or higher, the opticalfibers of this example exhibited a significantly improved lossvariation.

In general, the coefficient of linear expansion of silicon is about2×10⁻⁶ /° C., whereas that of ceramic is about 10×10⁻⁶ /° C. whensilicon is used for the waveguide, and ceramic is used for the opticalfiber connector, there results an about 1 μm of pitch deviation of thefitting pin V grooves at the interface in the case of a high or lowtemperature due to difference in coefficient of heat expansion betweenthe two materials. In order to compensate this, either the waveguidemodule or the optical fiber connector is warped, producing theconnection loss due to an axis deviation. The reason why the lossvariation was relatively small should be that the same material was usedfor the waveguide module and the optical fiber connector.

As described above, in this example, a waveguide module and an opticalfiber connector were made of materials having the same coefficient oflinear expansion. Therefore, a pitch deviation such as above does notoccur, thereby decreasing a loss variation caused by heat cycle.

EXAMPLE 6

This example was designed to confirm the result obtained in Example 5,and examine how a difference in coefficient of linear expansion has aninfluence on a loss variation. In the example, 10 types of optical fiberconnectors were prepared by using 10 types of glass ceramic materialseach having a coefficient of linear expansion from 1×10⁻⁶ /° C. to10×10⁻⁶ ° C. differing one from another by 1×10⁻⁶ /° C. The opticalfiber connectors thus manufactured were subjected to a heat cycle testat the same temperature as mentioned above. From this test, it wasconfirmed that the loss variation was within a range of ±0.2 dB with anoptical fiber connector made of glass ceramic having a coefficient oflinear expansion of 7×10⁻⁶ /° C.

Thus, it can be concluded that a loss variation depends mainly upon adifference in coefficient of linear expansion between materials used tomanufacture a waveguide module and an optical fiber connector. In thecase where the pitch of the V grooves 72 is about 4.6 mm, the lossvariation at a high or low temperature can be controlled by setting thedifference in coefficient of linear expansion between the waveguidemodule and the optical fiber connector at 7×10⁻⁶ /° C.

EXAMPLE 7

In place of a ceramic-made optical fiber connector discussed in Example2, an optical fiber connector made by plastic molding, such as shown inFIG. 19, was used in this example. The optical fiber connector used herewas of the same type as that generally used as a multi-core fiberconnector. As compared to those made by forming grooves thereon incutting process using a slicer, the production cost can be made low, andfurther mass production of such a plastic optical fiber connector can beeasily achieved. With the product of this example, the connection losswas an average of 0.5 B, with a maximum of 1 dB, per one connection.

EXAMPLE 8

In this example, a waveguide module was made of the same material asthat of the waveguide module discussed in Example 2. The fitting pinswere connected to both waveguide module and optical fiber connector bymeans of epoxy adhesive. Although the waveguide module and the opticalfiber connector of this example could not be detached from each other,the variance of the light output intensity caused by external factorssuch as vibration and the like could be made extremely small as 0.02 dBor lower.

Even in the case where the fitting pin was fixed to either the waveguidemodule or the optical fiber connector by means of adhesive, the varianceof the light output intensity caused by the external factors such asvibration and the like could be made smaller than the case where thefitting pin was not fixed.

As described above, according to the method of the present invention,markers are formed without embedding them, and alignment of fiber andwaveguide are carried out based on the position of each marker as areference. More specifically, the distance between a waveguide and aguide groove formed in a waveguide element is set to be exactly the sameas the distance between a corresponding optical fiber and acorresponding guide groove or hole, and therefore the waveguide and theoptical fiber can be connected at a high accuracy without actuallyaligning them with each other. Consequently, the time required forconnecting optical fibers can be significantly shortened. Further, themarker is not completely embedded, and a portion thereof can beobserved; therefore the marker can be easily remarked as a reference forpositioning.

Thus, an optical axis deviation between a waveguide and an optical fibercan be made small, and they can be optically connected at a low loss.Also, a waveguide part containing an waveguide element and an opticalfiber connector can be positioned with each other by inserting fittingpins into each other, and therefore the waveguide part itself can beused a type of detachable connector. As compared with a conventionalmethod in which a waveguide module and an optical fiber connector arefixedly connected with each other semi-permanently by means of adhesiveor the like, and an optical fiber projecting out in a pig-tail mannerfrom the waveguide part is connected to another optical fiber of anotherpart by the fusion connection technique, the connection loss can bereduced, and the housing space for a connection portion can be reducedaccording to the present invention.

Moreover, the difference in coefficient of linear expansion betweenmaterials used for preparing a waveguide module and an optical fiberconnector can be made no higher than a certain value in the invention;therefore the loss variance at a high or low temperature can besuppressed.

We claim:
 1. A method of connecting optical fibers and waveguides with each other, comprising the steps of:coating a lower clad layer formed on a first substrate with a waveguide material; patterning said waveguide material by a photolithography method so as to form:a plurality of parallel waveguides with a predetermined interval between adjacent waveguides; and a marker located at a predetermined distance away from a particular one of said waveguides; forming an upper clad layer on a region except where the marker is located so as to manufacture a light wave circuit; forming a first fitting pin groove having a V-shaped cross section for receiving a first fitting pin, therein, said fitting pin groove and said marker, thereby manufacturing a waveguide module; forming a plurality of optical fiber grooves on a second substrate for fixing a plurality of optical fibers therein; forming a second fitting pin groove or hole that is usable for alignment with said marker on said first substrate; fixing each of said plurality of optical fibers into respective ones of said plurality of optical fiber grooves, thereby manufacturing an optical fiber connector; and inserting the first fitting pin into the first fitting pin groove of said waveguide, and into the second fitting pin groove or hole so as to align the first and second substrates with each other, thereby connecting each of the optical fibers and each of the light wave circuits.
 2. A method of connecting optical waveguides and optical fibers according to claim 1, wherein a press cover is placed on at least one of the first and second substrates.
 3. A method of connecting optical waveguides and optical fibers according to claim 1, comprising finishing an end surface of the optical fiber connector so as to have a mirror-like finish.
 4. A method of connecting optical waveguides and optical fibers according to claim 1, comprising applying a matching agent on a to-be-connected surface of each optical fiber and to each waveguide of said light wave circuit.
 5. A method of connecting optical waveguides and optical fibers according to claim 1, wherein a coefficient of linear expansion of a material used for the waveguide module is substantially the same as a coefficient of expansion of the optical fiber connector.
 6. A method of connecting a plurality of optical fibers and a plurality of optical waveguides with each other, comprising the steps of:manufacturing the plurality of optical waveguides by:coating a lower clad layer formed on a first substrate with a waveguide material; patterning said waveguide material by a photolithography method so as to form a light wave circuit that has a plurality of parallel waveguides that correspond to a plurality of parallel optical fibers that are provided on a second substrate, said plurality of optical waveguides having a predetermined interval provided between adjacent parallel waveguides; forming at least one marker on said first substrate, said at least one marker being located at a predetermined distance away from a particular one of said plurality of optical waveguides; and forming an upper clad layer over the patterned waveguide material, on portions other than where said at least one marker is located on said first substrate, to facilitate an alignment of said plurality of waveguides with said plurality of optical fibers; and using said second substrate to manufacture an optical fiber core block by:forming a plurality of optical fiber grooves in said second substrate, each optical fiber groove having a V-shaped cross-section for respectively receiving and fixing therein one of said plurality of optical fibers; forming at least one marker-use groove having a V-shaped cross-section for facilitating alignment of said at least one marker on said first substrate with said second substrate; and setting said plurality of optical fibers into respective ones of said plurality of optical fiber grooves to thereby manufacture said optical fiber core block; and then aligning said at least one marker of the first substrate and said at least one marker-use groove of said second substrate with each other as the first and second substrates are brought into contact with each other so as to connect each of said plurality of optical fibers with a respective one of said plurality of optical waveguides.
 7. A method of connecting optical waveguides and optical fibers according to claim 6 wherein said first fitting pin groove is formed such that a center of a core of a light wave circuit is level with a center of the first fitting pin.
 8. A method of connecting optical waveguides and optical fibers according to claim 6, wherein the optical fiber connector is manufactured by a plastic molding process.
 9. The method of claim 6, wherein:said at least one marker formed on said first substrate comprises a plurality of markers; and said at least one marker-use groove comprises a plurality of marker-use grooves.
 10. The method of claim 9, wherein:said at least one marker on said first substrate comprises a linear marker; said at least one marker-use groove on said second substrate comprises a linear marker-use groove; and said at least one linear marker and said at least one linear marker-use groove, when aligned with each other, aligning the first and second substrates with each other. 